

const autoprefixer = require('autoprefixer');
const path = require('path');
const webpack = require('webpack');
const HtmlWebpackPlugin = require('html-webpack-plugin');
const ExtractTextPlugin = require('extract-text-webpack-plugin');
const ManifestPlugin = require('webpack-manifest-plugin');
const InterpolateHtmlPlugin = require('react-dev-utils/InterpolateHtmlPlugin');
const SWPrecacheWebpackPlugin = require('sw-precache-webpack-plugin');
const eslintFormatter = require('react-dev-utils/eslintFormatter');
const paths = require('./paths');
const getClientEnvironment = require('./env');

//Webpack uses `publicPath` to determine where the app is being served from.
//It requires a trailing slash, or the file assets will get an incorrect path.
const publicPath = paths.servedPath;
//Some apps do not use client-side routing with pushState.
//For these, "homepage" can be set to "." to enable relative asset paths.
const shouldUseRelativeAssetPaths = publicPath === './';
//Source maps are resource heavy and can cause out of memory issue for large source files.
const shouldUseSourceMap = process.env.GENERATE_SOURCEMAP !== 'false';
//`publicUrl` is just like `publicPath`, but we will provide it to our app
//as %PUBLIC_URL% in `index.html` and `process.env.PUBLIC_URL` in JavaScript.
//Omit trailing slash as %PUBLIC_URL%/xyz looks better than %PUBLIC_URL%xyz.
const publicUrl = publicPath.slice(0, -1);
//Get environment variables to inject into our app.
const env = getClientEnvironment(publicUrl);

//Assert this just to be safe.
//Development builds of React are slow and not intended for production.
if(env.stringified['process.env'].NODE_ENV !== '"production"') {
  throw new Error('Production builds must have NODE_ENV=production.');
}

//Note: defined here because it will be used more than once.
const cssFilename = 'static/css/[name].[contenthash:8].css';

//ExtractTextPlugin expects the build output to be flat.
//(See https://github.com/webpack-contrib/extract-text-webpack-plugin/issues/27)
//However, our output is structured with css, js and media folders.
//To have this structure working with relative paths, we have to use custom options.
const extractTextPluginOptions = shouldUseRelativeAssetPaths
  ? //Making sure that the publicPath goes back to to build folder.
  { publicPath: Array(cssFilename.split('/').length).join('../') }
  : {};

//This is the production configuration.
//It compiles slowly and is focused on producing a fast and minimal bundle.
//The development configuration is different and lives in a separate file.
module.exports = {
  //Don't attempt to continue if there are any errors.
  bail: true,
  //We generate sourcemaps in production. This is slow but gives good results.
  //You can exclude the *.map files from the build during deployment.
  devtool: shouldUseSourceMap ? 'source-map' : false,
  //In production, we only want to load the polyfills and the app code.
  entry: [require.resolve('./polyfills'), paths.appIndexJs],
  output: {
    //The build folder.
    path: paths.appBuild,
    //Generated JS file names (with nested folders).
    //There will be one main bundle, and one file per asynchronous chunk.
    //We don't currently advertise code splitting but Webpack supports it.
    filename: 'static/js/[name].[chunkhash:8].js',
    chunkFilename: 'static/js/[name].[chunkhash:8].chunk.js',
    //We inferred the "public path" (such as / or /my-project) from homepage.
    publicPath: publicPath,
    //Point sourcemap entries to original disk location (format as URL on Windows)
    devtoolModuleFilenameTemplate: info =>
      path
        .relative(paths.appSrc, info.absoluteResourcePath)
        .replace(/\\/g, '/'),
  },
  resolve: {
    //This allows you to set a fallback for where Webpack should look for modules.
    //We placed these paths second because we want `node_modules` to "win"
    //if there are any conflicts. This matches Node resolution mechanism.
    //https://github.com/facebookincubator/create-react-app/issues/253
    modules: ['node_modules', paths.appNodeModules].concat(
      //It is guaranteed to exist because we tweak it in `env.js`
      process.env.NODE_PATH.split(path.delimiter).filter(Boolean)
    ),
    //These are the reasonable defaults supported by the Node ecosystem.
    //We also include JSX as a common component filename extension to support
    //some tools, although we do not recommend using it, see:
    //https://github.com/facebookincubator/create-react-app/issues/290
    //`web` extension prefixes have been added for better support
    //for React Native Web.
    extensions: ['.web.js', '.mjs', '.js', '.json', '.web.jsx', '.jsx'],
    alias: {

      //Support React Native Web
      //https://www.smashingmagazine.com/2016/08/a-glimpse-into-the-future-with-react-native-for-web/
      'react-native': 'react-native-web',
    },
  },
  module: {
    strictExportPresence: true,
    rules: [
      //TODO: Disable require.ensure as it's not a standard language feature.
      //We are waiting for https://github.com/facebookincubator/create-react-app/issues/2176.
      //{ parser: { requireEnsure: false } },

      //First, run the linter.
      //It's important to do this before Babel processes the JS.
      {
        test: /\.(js|jsx|mjs)$/,
        enforce: 'pre',
        use: [
          {
            options: {
              formatter: eslintFormatter,
              eslintPath: require.resolve('eslint'),

            },
            loader: require.resolve('eslint-loader'),
          },
        ],
        include: paths.appSrc,
      },
      {
        //"oneOf" will traverse all following loaders until one will
        //match the requirements. When no loader matches it will fall
        //back to the "file" loader at the end of the loader list.
        oneOf: [
          //"url" loader works just like "file" loader but it also embeds
          //assets smaller than specified size as data URLs to avoid requests.
          {
            test: [/\.bmp$/, /\.gif$/, /\.jpe?g$/, /\.png$/],
            loader: require.resolve('url-loader'),
            options: {
              limit: 10000,
              name: 'static/media/[name].[hash:8].[ext]',
            },
          },
          //Process JS with Babel.
          {
            test: /\.(js|jsx|mjs)$/,
            include: paths.appSrc,
            loader: require.resolve('babel-loader'),
            options: {

              compact: true,
            },
          },
          //The notation here is somewhat confusing.
          //"postcss" loader applies autoprefixer to our CSS.
          //"css" loader resolves paths in CSS and adds assets as dependencies.
          //"style" loader normally turns CSS into JS modules injecting <style>,
          //but unlike in development configuration, we do something different.
          //`ExtractTextPlugin` first applies the "postcss" and "css" loaders
          //(second argument), then grabs the result CSS and puts it into a
          //separate file in our build process. This way we actually ship
          //a single CSS file in production instead of JS code injecting <style>
          //tags. If you use code splitting, however, any async bundles will still
          //use the "style" loader inside the async code so CSS from them won't be
          //in the main CSS file.
          {
            test: /\.css$/,
            loader: ExtractTextPlugin.extract(
              Object.assign(
                {
                  fallback: {
                    loader: require.resolve('style-loader'),
                    options: {
                      hmr: false,
                    },
                  },
                  use: [
                    {
                      loader: require.resolve('css-loader'),
                      options: {
                        importLoaders: 1,
                        minimize: true,
                        sourceMap: shouldUseSourceMap,
                      },
                    },
                    {
                      loader: require.resolve('postcss-loader'),
                      options: {
                        //Necessary for external CSS imports to work
                        //https://github.com/facebookincubator/create-react-app/issues/2677
                        ident: 'postcss',
                        plugins: () => [
                          require('postcss-flexbugs-fixes'),
                          autoprefixer({
                            browsers: [
                              '>1%',
                              'last 4 versions',
                              'Firefox ESR',
                              'not ie < 9', //React doesn't support IE8 anyway
                            ],
                            flexbox: 'no-2009',
                          }),
                        ],
                      },
                    },
                  ],
                },
                extractTextPluginOptions
              )
            ),
            //Note: this won't work without `new ExtractTextPlugin()` in `plugins`.
          },
          //"file" loader makes sure assets end up in the `build` folder.
          //When you `import` an asset, you get its filename.
          //This loader doesn't use a "test" so it will catch all modules
          //that fall through the other loaders.
          {
            loader: require.resolve('file-loader'),
            //Exclude `js` files to keep "css" loader working as it injects
            //it's runtime that would otherwise processed through "file" loader.
            //Also exclude `html` and `json` extensions so they get processed
            //by webpacks internal loaders.
            exclude: [/\.js$/, /\.html$/, /\.json$/],
            options: {
              name: 'static/media/[name].[hash:8].[ext]',
            },
          },
          //** STOP ** Are you adding a new loader?
          //Make sure to add the new loader(s) before the "file" loader.
        ],
      },
    ],
  },
  plugins: [
    //Makes some environment variables available in index.html.
    //The public URL is available as %PUBLIC_URL% in index.html, e.g.:
    //<link rel="shortcut icon" href="%PUBLIC_URL%/favicon.ico">
    //In production, it will be an empty string unless you specify "homepage"
    //in `package.json`, in which case it will be the pathname of that URL.
    new InterpolateHtmlPlugin(env.raw),
    //Generates an `index.html` file with the <script> injected.
    new HtmlWebpackPlugin({
      inject: true,
      template: paths.appHtml,
      minify: {
        removeComments: true,
        collapseWhitespace: true,
        removeRedundantAttributes: true,
        useShortDoctype: true,
        removeEmptyAttributes: true,
        removeStyleLinkTypeAttributes: true,
        keepClosingSlash: true,
        minifyJS: true,
        minifyCSS: true,
        minifyURLs: true,
      },
    }),
    //Makes some environment variables available to the JS code, for example:
    //if (process.env.NODE_ENV === 'production') { ... }. See `./env.js`.
    //It is absolutely essential that NODE_ENV was set to production here.
    //Otherwise React will be compiled in the very slow development mode.
    new webpack.DefinePlugin(env.stringified),
    //Note: this won't work without ExtractTextPlugin.extract(..) in `loaders`.
    new ExtractTextPlugin({
      filename: cssFilename,
    }),
    //Generate a manifest file which contains a mapping of all asset filenames
    //to their corresponding output file so that tools can pick it up without
    //having to parse `index.html`.
    new ManifestPlugin({
      fileName: 'asset-manifest.json',
    }),
    //Generate a service worker script that will precache, and keep up to date,
    //the HTML & assets that are part of the Webpack build.
    new SWPrecacheWebpackPlugin({
      //By default, a cache-busting query parameter is appended to requests
      //used to populate the caches, to ensure the responses are fresh.
      //If a URL is already hashed by Webpack, then there is no concern
      //about it being stale, and the cache-busting can be skipped.
      dontCacheBustUrlsMatching: /\.\w{8}\./,
      filename: 'service-worker.js',
      logger (message) {
        if(message.indexOf('Total precache size is') === 0) {
          //This message occurs for every build and is a bit too noisy.
          return;
        }
        if(message.indexOf('Skipping static resource') === 0) {
          //This message obscures real errors so we ignore it.
          //https://github.com/facebookincubator/create-react-app/issues/2612
          return;
        }
        console.log(message);
      },
      minify: true,
      //For unknown URLs, fallback to the index page
      navigateFallback: publicUrl + '/index.html',
      //Ignores URLs starting from /__ (useful for Firebase):
      //https://github.com/facebookincubator/create-react-app/issues/2237#issuecomment-302693219
      navigateFallbackWhitelist: [/^(?!\/__).*/],
      //Don't precache sourcemaps (they're large) and build asset manifest:
      staticFileGlobsIgnorePatterns: [/\.map$/, /asset-manifest\.json$/],
    }),
    //Moment.js is an extremely popular library that bundles large locale files
    //by default due to how Webpack interprets its code. This is a practical
    //solution that requires the user to opt into importing specific locales.
    //https://github.com/jmblog/how-to-optimize-momentjs-with-webpack
    //You can remove this if you don't use Moment.js:
    new webpack.IgnorePlugin(/^\.\/locale$/, /moment$/),
  ],
  //Some libraries import Node modules but don't use them in the browser.
  //Tell Webpack to provide empty mocks for them so importing them works.
  node: {
    dgram: 'empty',
    fs: 'empty',
    net: 'empty',
    tls: 'empty',
    child_process: 'empty',
  },
};
